The Metropolitan Police has now confirmed the nerve agent was found in the blood sample of another officer. The force said the Wiltshire Police officer, who does not wish to be identified, displayed signs at the time that indicated exposure to a very small amount of Novichok. The officer received medical treatment and returned to duties shortly afterwards.

Detectives from the Counter Terrorism Policing (CTP) network said a forensic examination of the officer's blood has now confirmed that traces of Novichok were in the sample. The officer is the sixth person to be confirmed through forensic testing as a victim of the Salisbury attack.

Mr Skripal and his daughter recovered after intensive care in hospital, and their current whereabouts are being kept secret.

Det Sgt Bailey needed hospital treatment but returned to full active duty two months after the attack.

Dawn Sturgess was fatally poisoned after suffering high levels of exposure to Novichok in nearby Amesbury in June 2018. Ms Sturgess and her partner Charlie Rowley - who was also contaminated but has since recovered - are believed to have come into contact with a bottle of Novichok discarded by the Skripals' attackers.

A UK investigation blamed Russian agents for the Novichok attack, identifying two suspects using the names Alexander Petrov and Ruslan Boshirov. Both deny any involvement.

The attack prompted the UK and its Western allies to expel many Russian diplomats, with Russia retaliating with its own expulsions.